1. Field of the Invention
The present invention generally relates to powering and maintaining power controlled power systems and, more particularly, to powering and maintaining power controlled aircraft power systems protected by electronic circuit breakers.
2. Background Description
Typical commercial transport aircraft include multiple, complex electrical systems with hundreds of circuit breakers protecting those systems from over-current conditions, traditionally, with Thermal Circuit Breakers (TCB). Thermal circuit breakers normally trip open to protect circuits when enough current passes through the breaker to heat the breaker above a trip point. Additionally, a thermal circuit breaker may be manually opened by pulling on a push/pull breaker switch prior to maintenance, in order to prevent equipment from becoming energized and causing damage, injury, or death. Frequently, tags and locks are attached to open circuit breakers to convey important safety information, and to prevent dangerous closures. Once maintenance is complete, tags and locks must be removed, and the thermal circuit breakers must be manually closed by depressing the push/pull breaker switch. Typical thermal circuit breakers are relatively heavy and require substantial additional aircraft wiring. Since, these heavy thermal circuit breakers are far from optimum or efficient, for this and for many other reasons, some aircraft manufacturers have turned to solid state technology.
Instead, these aircraft manufacturers are replacing heavy thermal circuit breakers with remotely located, Solid State Power Controllers (SSPCs) or Electronic Circuit Breakers (ECBs) for improved circuit protection, ease of use and improved personnel safety. A typical state of the art ECB mimics the states of a standard TCB, i.e., closed, opened/tripped, or locked out. Typically, an internal local processor controls each ECB. A centralized interface processor provides control signals over a data bus to coupled ECBs. Each selected ECB switches states in response these control signals and, may respond to the centralized interface processor with an electrical signal that indicates its current breaker state. ECB state information, including electronic representations of tags and locks, is normally stored in internal ECB non-volatile storage. Since ECBs are electronically controlled by the processor, they can be controlled from any processor interface, regardless of the actual ECB location. So, for example, mechanics, pilots, or other users can remotely determine and change the current state of ECBs without leaving the aircraft flight deck.
Unfortunately, without electrical power, the breaker state is unknown. Because they are fully electronic/electronically controlled, the ECB must have electrical power to view or alter the current ECB state. This can cause problems when electrical power is initially applied or restored. For example, when the airplane is unpowered, a mechanic is not able to open an unpowered ECB prior to a maintenance activity. If the mechanic proceeds with the activity and, subsequently, power is applied to the airplane, the equipment being maintained could be inadvertently powered. This is a hazardous condition, and consequently, could lead to injury or death to the mechanic, or could cause damage to the airplane.
Additionally, if an ECB is replaced during maintenance, the internal state data may be lost or disturbed. This could have the same hazardous consequences, i.e., protected equipment could become inadvertently powered. Furthermore, many ECBs are normally integrated together in a single Line Replaceable Module, (LRM). So, replacing a single such module could impact many individual ECBs and, therefore, many different airplane systems.
Accordingly, there is a need for monitoring and inspecting aircraft electronic circuits during maintenance procedures even in unpowered aircraft and especially during power distribution system maintenance. More particularly, there is a need to allow maintenance personnel to engage in such activity without risking damage to the aircraft, and while protecting personnel from injury or death.